All scholars agree that the place name Cedeira derives from a pre-existing Latin word
cetaria, which alludes to marine fish. As no coinciding words seem to exist in the traditional lexical heritage of Galicia nor does it seem to have ever existed as a common name in the
Gallaecian language, the toponym is most likely from the Roman period. However, the hypothesis that the name and the town of Cedeira have Roman origins cannot be confirmed categorically, owing to lack of historical documentation. The question is, does 'Cedeira' derive from a classical Latin noun or a later vulgar homonym of the late Empire. The first possibility is that it derives from the substantive neuter plural of classical Latin, which, like the feminine cetariae, meant 'ponds or nurseries where large fish are raised'. The more credible alternative is that it comes from a late Latin feminine adjective
cetaria, formed from
cetus – whale or large fish – +
arius, which combined would mean "petaining to whales or large fish", because of the abundance of Galician names that contain the suffix
-eiro or
-eira come normally from adjectives. The oldest documented mention of the place appears in a document from 868, which reads: If the name of the town was originally an adjective applied to a generic name –villa or terra, it would be used in adjectival agreement, as in a document from 1111: {{Translated blockquote |language=la Before the 12th century, this toponym had to undergo several more phonetic changes into the
Romance language form of the name appeared in a document from 1114, The initial
i can be attributed to an unfruitful phonetic change, repeated in the spelling of the hamlet, , as Filgosa. That certainly also seems to have occurred in the case of
Torrecedeira, in
Pontevedra, one of the four other known 'Cedeiras' in Galicia, that are also all located on the coast, where the sighting of cetaceans, such as whales, or large marine fish, was not unusual. Finally, in support of the toponym
Cedeira signifying the presence of whales or large fish in the estuary and off the coast, this Cedeira is only the largest of four , which are all spots located on the coast of the autonomous community, from where the sighting of cetaceans – i.e. large marine animals – was common even in the 18th century. ==Parroquias==